1. Field of the Invention
The present invention relates to a resin-made fuel tank for a vehicle, and more specifically, a part fixing structure and a part fixing method to such a resin-made fuel tank.
2. Description of the Related Art
Prior arts of fixing a tank-associated part to a resin-made fuel tank are disclosed in JP 2009-132297 A and JP 2008-507651 A. JP 2009-132297 A discloses a technique for forming a part so as to have an abutting face that closely contacts an internal face of a tank wall of a fuel tank and to have a protrusion protruding from the abutting face and having a triangular cross section. The protrusion is allowed to enter in the interior of the tank wall, thereby fixing the part to the tank wall. JP 2008-507651 A discloses a technique for forming a part so as to have an orifice, and a melted resin of a tank wall is caused to flow into a recess of a core (a counter molding part) through the orifice, thereby fixing the part to the tank wall with the flowed resin portion being as a rivet-like engaging portion.
According to JP 2009-132297 A, since the protrusion of the part has a triangular cross section which gradually tapers toward the tip, it is difficult to obtain mechanical coupling force to the tank wall. In contrast, according to JP 2008-507651 A, since the portion of the resin of the tank wall serves as the rivet-like engaging portion, the part is firmly fixed to the tank wall because of mechanical coupling force by the engaging portion.
According to JP 2008-507651 A, however, in order to allow the resin of the tank wall to efficiently flow into the orifice, it is necessary to provide, at a die side, a convex portion which protrudes into the orifice, and in order to form a rivet-like engaging portion, it is also necessary to form a recess at a core side. Therefore, there arises a problem that the configuration of the molding die for a fuel tank becomes complex.
Moreover, According to JP 2008-507651 A, since the total cubic volume of sheet-like parison layers (i.e., HDPE layers 2, 2′, and an EVOH layer 3) are predetermined, when a resin is poured into the recess of the core in order to form a rivet-like portion (i.e., a plateau portion 8), the layer other than the rivet-like portion should be partially thin by what corresponds to the flowed resin. Hence, in the case of the structure disclosed in FIG. 1 of JP 2008-507651 A, for example, it is necessary in some cases to make the layer of a portion along the inclined face of the convex portion of the die to be thin. From the standpoint of the strength of the tank and of the fuel impermeable characteristic, it is not desirable that a thin layer is partially formed as described above.
The present invention has been made in view of the foregoing circumstances, and it is an object of the present invention to provide a part fixing structure and a part fixing method to a resin-made fuel tank which can firmly fix a part to a tank wall without the need of providing a convex portion and a recess on a molding die.